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Thread: 2006 Audi S4 Avant Manual missfire issues

  1. #11
    Benevolent Dictator Uwe's Avatar
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    Quote Originally Posted by cdsjklee View Post
    someone told me my S4 may have clogged cat. but I do not have any CEL for Clogged cat or oxygen sensor. what do you guys think?
    it gets worse as temp goes up.
    Remove before-CAT oxygen sensor and use a bore-scope "snake" camera to do a visual inspection? Those things are pretty cheap now; many will work with a smart-phone:
    https://www.amazon.com/s?k=endoscope

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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    Removed Bank 1 cat (passenger side), It looks OK.
    Do not see any broken pieces and I did shake the cat no rattling sound.
    but as I mention before Bank 1 side exhaust is very weak compare to Driver side. Exhaust out put should be same on both side or is it normal to have ones side a lot more stronger than other side ?
    I connected vacuum to Pre cat side of pipe and checked to see any air movements through the pipe.
    it does move air but very of weak I am not sure how strong it should move air . Is there a better way to check if cat is clogged ?

  3. #13
    Benevolent Dictator Uwe's Avatar
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    Quote Originally Posted by cdsjklee View Post
    Exhaust out put should be same on both side or is it normal to have ones side a lot more stronger than other side ?
    I would also expect it to be close to equal, but I do not have a good mental (or any other kind of) picture of this exhaust system. Is it fully separate or are there one or more cross-overs or common paths?

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

  4. #14
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    looks like they are fully separated.
    found picture here.https://forum.rs246.com/viewtopic.php?t=126582

  5. #15
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    looks like they are fully separated.
    found picture here.https://forum.rs246.com/viewtopic.php?t=126582
    https://i.imgur.com/vGa1C.jpg[/IMG]

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  7. #16
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    Have the front pre-CAT Lambda sensors been changed? Most pre-CAT Lambda sensors are only good for about 50K-60K miles then they get sluggish.
    You mention you have changed many parts on this engine but do not mention replacing these sensors.
    Maybe one has been replaced previously and is working OK while the other is sluggish.
    The car ignores these sensors until the engines has warmed-up so if it runs OK cold, this could be another pointer towards the Lambda sensors.

    I also recommend performing a compression test on each cylinder. I have seen hairline cracks in the head cause similar issues once the engine gets hot.

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